It is known a spiral fluted tap which includes (a) a threaded portion having an external thread corresponding to an internal thread to be cut and a cutting edge formed along a spiral flute formed to divide the external thread, and (b) being screwed into a prepared hole that is provided on a workpiece to cut an internal thread by the cutting edge on an inner circumferential surface of the prepared hole with discharging chips toward a shank via the spiral flute (See Patent Document 1).    Patent Document 1: JP 8-39353 A